Grinding wheel



Feb. 6, 1940. VAN DER PYL 2,189,259

GRINDING WHEEL Filed May 19, 1938 EDWFIHD VFIN DER PYL.

Patented F b'. 6, 1940 PATENT oFFlcE GRINDING WHEEL Edward Van der Pyl,Holden, Mass., assignor to Norton Company, Worcester, Mass., acorporation of Massachusetts Application May 19, 1938, Serial No.208,859

1 Claim.

The invention relates to grinding wheels, and with regard to its morespecific features to dia mond grinding wheels.

One object of the invention is to provide a superior cutting-on wheel.Another object of 'the invention is to make an extremely durable diamondgrinding wheel. Another object of the invention is to make a hard bondeddiamond .1 grinding wheel. Another object of the invention is to producean abrasive wheel of long life and tough characteristics Another objectof the invention is to provide an integral wheel the center portion ofwhich is metal and the outer portion of which is metal containingabrasive. Other objects will be in part obvious or in part pointed outhereinafter. I

The invention accordingly consists in the features of construction,combinations of elements, arrangements of parts, and in the severalsteps and relation and order of each of said steps to one or more of theothers .thereof, all as will be illustratively described herein, and thescope of the application of which will be indicated in the followingclaim.

25 In the accompanying drawing showing one of many possible embodimentsof the mechanical features of this invention,

Figure 1' is a side view of a diamond wheel manufactured according tothe invention;

30 Figure 2 is a cross sectional view taken on th line 2-2 of Figurefl;

Figure 3 is a cross sectional view of mold'parts into which has beenplaced the material forming the center of the wheel;

35 Figure 4 is a cross sectional view of the mold subsequent to theincorporation of the abrasiv material; and

Figure 5 is a cross sectional view of the mold after it has been closed.

40 I provide a quantity of copper in powdered form. This may beelectrolytic copper, if desired, or it may be produced in any othersuitable manner but preferably it should be relatively pure andfinely-dividedj That is to say, I prefer to use 45 powder finer than 200mesh size and the impalpable flours give excellent results in actualpractice.

form and the foregoing specification as to' purity 50 and finenessequally apply. I then make a mixture of the tin and copper powders andas an example of a mixture which I now prefer, I use 18.6% (by weight)of tin, the remainder copper. It should be understood, however, that Imay use 55 any of the'alloy mixtures specified in my prior I provide aquantity of tin also in powdered Patent No. 2,072,051. So far as broadfeatures of the invention are concerned, I may use any other metalpowders. The mixing of the powders is usually accomplished by placingthe measured amounts ma 5 cylindrical glass'jar and placing the jar on apair of parallel rollers rotating in the same direction to revolve thejar. The jar may be left on the rollers for two or three hours andrequires no attention and at the end of that time the powders are foundto be very thoroughly mixed.

Referringnow to Figuresl and 2, the completed cutting-off wheelcomprises a central portion III of pressed and sintered metal powder andan outer portion II of pressed and sintered metal powder containingdiamonds, therebeing a central hole I2 in the wheel for mounting on aspindle. The central non-abrasive portion I0 may-be somewhat thinnerthan the outer abrasive portion II to provide good clearance in acuttingoff operation.

Referring now to Figure 3, 'I provide a mold bottom I5 which is acylinder with a central hole. I further provide a mold ring I6 and acentral plug I1. Putting the parts together as shown in Figure 3 (thering I6 may be held up by shims, not shown), I fill the space inside ofthe mold ring I6 with a measured amount of the mixture of copper and tinpowders Illa. I level this off carefully by means of hand scrapers orthe like.

Referring now to Figure 4, I provide a. mold top plate I511, which isidentical with the bottom plate I5. I also provide an outer mold ringI9. I place the top plate I5a on top of the mixture Illa and place theouter mold ring I9 around the inner mold ring I6. I then fill the spacebetween the top plate I5a and the mold ring I9 with a mixture of the twometal powders and diamonds or other abrasive. I then insert an upperinner mold ring Ilia. inside the outer mold ring I9, as

' shown in Figure 4. I then take the entire mold.

to a press and close the mold to'the position shown in Figure 5. Afterthe mold is closed, the plug I! may readily be pressed out and the outermold ring I9 maybe readily stripped, after which the rest of the moldreadily separates.

The result is a wheel as shown in Figures 1 and 2 and when considerablepressures are used, this wheel has considerable strength. However,

I prefer to heat treat the wheel which causes the metal particles tosinter together and makes the entire wheel stronger and the bond for thediamonds somewhat more brittle. I may sinter at a temperature which willnot burn the diamonds and indeed even below the red heat temperature ofthe metal powders employed. The eflect of metallurgical change in thestructure of the wheel so that the final product is an integral piece ofconsiderable strength and the diamonds are held in place for a long timeso that substantially their entire abrasive life is utilized.

Considering now more specifically the exact proportions of theingredients, the abrasive annulus ll consists of 25% by volume ofdiamonds, the remainder metal bond of which 18.6% is tin and 81.4% iscopper. The central portion l consists of 18.6% tin and 81.4% copper.However, the

amount of mixture Illa is calculated suchthat the central portion 10will be from to 15% denser, than the abrasive portion II. This involvesexistence of a certain amount of porosity in the outer portion ll priorto the sintering. The sintering causes the various portions of the wheelto shrink very slightly, approximately to the actual specific gravity ofthe alloy and to a body with substantially no porosity. I have foundthat for the thicker wheels a lesser amount of difference in densitywill suflice for good results. That is to say, the thinner the wheelproportionate to its diameter, the greater the difierence in density. Awheel of the proportions shown in Fi ures 1 and 2 may be satisfactorilymanufactured with a diiference in density of Very thick wheels mayrequire a difference in density of no more than 5%.

"From actual experience in manufacture I have found that, especially forthe thin wheels, a difference in density of the two sections of thewheel prevents the separation of the two portions into separate piecesand also warpingof the center portion. In fact, my experience has beenthat wheels of the proportions indicated in the drawing could notbesuccessfully made with the center portion of equal density with theouter portion. First attempts to make the wheel described herein,accordingto which the density was uniform throughout, resulted infailures.

Industry at present uses a large quantity of cemented carbide cuttingtools in turret lathes, boring mills and many other machine tools. Owingto the great hardness of this material, it has been difficult to workit. Heretofore resinoid bonded diamond wheels have been used for cut--ting up rods into small tool portions, but this practice has beenabandoned bysome owing to the high cost of the wheels. In the use ofresinoid bonded diamond grinding wheels of a shape somewhat like thewheel of Figures 1 and 2, only slight pressures could be used sinceotherwise the wheel would buckle. It is believed that these resinoidbonded wheels wore out long beiorev the entire cutting life of thediamonds had been used. In other words, the bond released the diamondsbefore they had become dulled. The diamond abrasive bond structureaccording to my Patent No. 2,072,051, one example. of which is theabrasive structure according to the present invention, is

harder than resinoid, is tough and to some extent brittle, and thediamonds are held much longer. I believe that I hold the diamonds inplace under most conditions of operation for a large portion of theiruseful life, that is to say until they have become somewhat dulled.Using a cutting-01f wheel as shown in Figures 1 and 2, considerablepressure may be applied as the wheel is comparatively strong and thebond is comparatively hard. Accordingly, a cutting-off operation takesvery much less time using the wheel of the present invention than it didusing prior resinoid bonded diamond cut off wheels. Furthermore, thewheel Wear in such a cutting-off operation is very much less.

While the cutting-off wheel is an outstanding example of a successfulembodiment of my invention, it should be understood that the inventionis in no wise limited thereto since other types of peripheral abradinggrinding wheels can be made according to the invention and so far as.

certain features are concerned, the invention may be embodied in acup-shaped wheel or other type of wheel the side face of which is theabrasive portion. Furthermore, so far as certain features of theinvention are concerned, it may be embodied in wheels the abrasive ofwhich is other than diamond, for example alumina, silicon carbide orboron carbide.

The pressing of the wheel of the invention may be done in a hydraulicpress using a pressure of the order of 2500 pounds to the square inch.The sinteringmay be done at a temperature of 550 C. I may in some casesuse in the sintering furnace a non-oxidizing atmosphere, for example areducingatmosphere (hydrogen) or nitrogen or an inert atmosphere, forexample argon. This, however is a further precaution and in the case ofthe specific bond specified above and a temperature of 550 C. anexcellent wheel can be made without this precaution. For furtherdisclosure of bonds which can be used with good effect and for furtherdirections in pressing and sintering, reference may be made to my priorPatent 2,072,051 previously referred to.

As an example of comparative results for wheels made according to thepresent invention and resinoid bonded diamond wheels, I caused wheels tobe prepared according to the following specifications:

Resinoid bonded wheel dehyde produced according to standard methods by awell known manufacturer. After the wheel was pressed, it was baked fortwelve hours at 160 C. to polymerize the resin.

' Metal bonded wheels Three metal bonded wheels were made up ofdimensions the same as the resinoid bonded wheel, that is to say 4" indiameter, .040" thick,

with hole. These wheels were likewise made from 100 grit diamond grainwithstandard concentration, namely diamonds by volume. Likewise diamondsoccupied A, in the periphery.

Wheel A .Wheel A consisted of 81.4% copper, 18.6% tin, sintered in areducing atmosphere at 550 C.

Wheel B Wheel B consisted of 76.8% copper, 19.2% tin,

and 4.0% nickel sintered in a reducing atmosphere at 550 C. I

' Wheel 0 Wheel C consisted of 72.4% copper, 13.2% tin and 14.4% nickelsintered in a reducing atmosphere at 550 C.

In the foregoing as well as the previous description, the percentages ofthe ingredients of the 15 alloy are by weight while the percentage ofdiamonds to bond is by volume, since it is easier to make calculationsthis way. In the case of wheels.

A, B and C the central portion was pressed to a ten percentgreaterdensity than the outer portion in accordance with previousdescription.

Y Probably in these cases the porosity of the inner portion afterpressing is only two or three per cent by volume and after sintering,the entire article virtually lacks porosity. The following table showsthe results of tests under uniform conditions of the above wheelsz' Wear:2 WheelA WheeiB WheeiC Cutting glass .0062" .0005 .0008" Cuttingcemented tungsten mrblde .0223" .0024" .0043" The formation of a centerportion'of integral structure with the peripheral abrasive portion andof strong metal permits the utilization to the best advantage of theabrasive qualities of metal bonded diamond grinding composition,especially in a thin cutting-off wheel where strength to resist thegrinding pressure which results in radial and lateral stresses is of theutmost importance.

Wheels manufactured according to'the present invention are unitarywheelsand are metallurgically unitary in the sense that the individual metalparticles out of which the wheel was made cannot be identified, havelosttheir separate existence, and the entire wheel including the abrasiveportion as well as the center portion is jointless and seamless and thecrystalline structure of the metal is notbroken by the originalboundaries of the particles which were used to.

make it. In other words, the particles have grown together into a solidpiece.

It will thus be seen that there has been provided by this invention anarticle and a method in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As various possible embodiments might bemade'of the mechanicalfeatures of the above invention and as the art herein described might bevaried in various parts, all without departing from the scope of theinvention, it is to he understood that all matter hereinbefore set forthor shown in the accompanying drawing is to be interpreted asillustrative and not in a limiting sense.

ation the inner part is between 5 and 15%denser so than the outer part,closing the mold, then sintering at a temperature below the meltingpoint of the metal. a

EDWARD VAN DER. PYL.

